This invention relates generally to an improvement in mops used by roofers to spread hot tar, and more specifically to an improvement in glass mop heads.
In the roofing of many buildings, especially commercial structures, hot tar or asphalt, referred to in the trade as "hot stuff", is widely used as a binder and sealant and must be heated to temperatures of about 400.degree. to 500.degree. F. in order to be thin enough to spread. The "hot stuff" is generally mopped on the roof by hand. The mops which are used to mop on the "hot stuff" must be able to stand up to rigorous requirements both as to tensile and abrasive strength and as to resistance to high temperatures.
For clarity, the following terms, as used herein, are defined:
(1) a fiber or filament is the most basic element of the composite yarn, being extruded, drawn, spun or otherwise formed into a single elongated element;
(2) twisted means wound or wrapped around each other. Twisting imparts a spiral or circular form, as by turning at either end.
Cotton, and to a very limited extent rayon--another cellulosic type fiber, is by far the most commonly used mop yarn. The yarns are somewhat bulky or "full-bodied" with low density and, therefore, a bulky mop head can be made weighing only about two and one-half to three pounds. A problem, however, is that cotton mop heads have a relatively short useful life, usually lasting only one full day of work. This short life is due to a combination of factors including particularly abrasive wear on the yarns and high tar temperatures.
Yarns comprising glass fibers are also used to make mopheads, but prior art mopheads fabricated from glass fibers comprise a much smaller share of the market than do cotton mop heads. The glass yarns in mop heads have a higher tensile and abrasive strength than cotton yarns and a higher resistance to increased temperatures. However, glass yarns used in prior art mop heads are less "full bodied" having a greater density than cotton yarns, and, therefore, many more glass yarns must be used to achieve a mop head of the same bulk as a cotton mop head. The prior art yarns of glass fibers will not hold as much of the "hot stuff" per pound as will the cotton yarns, apparently because the glass has a smoother surface with a lower coefficient of friction. Therefore, more glass must be used in the mop head to hold the same bulk of "hot stuff" as a typical cotton mop. As a result, the prior art glass yarn mop heads have the disadvantages of being expensive and very heavy. For example, a typical prior art glass mop head must weigh seven or eight pounds or more and include approximately 11,000 yarns to achieve the same bulk as a two or three pound cotton mop. A thirty inch sample of a single twisted yarn used in this typical prior art glass mophead weighs approximately 0.30 grams (0.00066 lbs.).